In university classrooms a suitable acoustic condition is necessary to enhance the productivity of students and the vocal comfort of lecturers. With this purpose international standards recently introduced new requirements on the quality of verbal communication. The goal of this work is to propose a procedure for predicting speech intelligibility in large learning spaces through geometrical acoustic simulations. The performance of the present approach is investigated using analytical prediction models as well as the measurements results in six university classrooms surveyed.

Sound absorbing micro-perforated panels (MPPs) are being increasingly used because of their high quality in terms of hygiene, sustainability and durability. The present work investigates the feasibility and the performance of MPPs when used as an acoustic treatment in lecture rooms. With this purpose, three different micro-perforated steel specimens were first designed following existing predictive models and then physically manufactured through 3D additive metal printing. The specimens’ acoustic behavior was analyzed with experimental measurements in single-layer and double-layer configurations. Then, the investigation was focused on the application of double-layer MPPs to the ceiling of an existing university lecture hall to enhance speech intelligibility. Numerical simulations were carried out using a full-spectrum wave-based method: a finite-difference time-domain (FDTD) code was chosen to better handle time-dependent signals as the verbal communication. The present work proposes a workflow to explore the suitability of a specific material to speech requirements. The measured specific impedance complex values allowed to derive the input data referred to MPPs in FDTD simulations. The outcomes of the process show the influence of the acoustic treatment in terms of reverberation time (T30) and sound clarity (C50). A systematic comparison with a standard geometrical acoustic (GA) technique is reported as well.

Italian Historical Opera Houses are private or public spaces built around a cavea, with tiers of boxes on the surrounding walls. At the early age – from 16th to 18th century – boxes were private properties of the richest class, typically the financial responsible of the whole building. The stalls hosted the middle class, that gradually increased its social position and for this reason the wooden seats were progressively replaced by chairs. The gallery was reserved to lower classes. Does this social division correspond to a different acoustic comfort? The present work tries to answer this question using subjective preference models provided by scholars. With this aim, the room criteria defined by different authors and in distinct times are lined up with the ISO 3382 standards and analysed depending on the acoustic peculiarities of an Italian Historical Opera House selected as case study. Calibrated impulse responses were handled through the numerical simulations of a whole orchestra of virtual sound sources in the pit.

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The construction of a new worship space in cross-laminated timber provides a good opportunity to include acoustic needs in the whole design development. The surface porosity and the lightweight of wooden elements may be carefully considered in order to improve the intelligibility of priests' voice. In this work, a practical approach for obtaining a global acoustic comfort using sustainable materials is provided, using geometrical acoustic simulations. Material properties and architectural geometries were taken into account in order to evaluate subjective reverberation, speech intelligibility, and spatial perception over the whole audience. Results show how the sound energy distribution in the case study follows the sound field models proposed by scholars and how the ceiling shape-inspired by industrial sheds-contributes to the acoustic comfort of the faithfuls.

Wave-based techniques for room acoustics simulations are commonly applied to low frequency analysis and small-sized simplified environments. The constraints are generally the inherent computational cost and the challenging implementation of proper complex boundary conditions. Nevertheless, the application field of wave-based simulation methods has been extended in the latest research decades. With the aim of testing this potential, this work investigates the feasibility of a finite-difference time-domain (FDTD) code simulating large non-trivial geometries in wide frequency ranges. A representative sample of large coupled-volume opera houses allowed demonstration of the capability of the selected FDTD model to tackle such composite geometries up to 4 kHz. For such a demanding task, efficient calculation schemes and frequency-dependent boundary admittances are implemented in the simulation framework. The results of in situ acoustic measurements were used as benchmarks during the calibration process of three-dimensional virtual models. In parallel, acoustic simulations performed on the same halls through standard ray-tracing techniques enabled a systematic comparison between the two numerical approaches highlighting significant differences in terms of input data. The ability of the FDTD code to detect the typical acoustic scenarios occurring in coupled-volume halls is confirmed through multi-slope decay analysis and impulse responses' spectral content.

Acoustic metamaterials (AMMs) are designed with complex geometrical shapes to obtain unconventional sound-absorbing performances. As additive manufacturing is particularly suited to print complex structures in a more straightforward and controllable way, AMMs often exploit three-dimensional (3-D) printing techniques. However, when exposed to different temperature conditions, such structures can be affected by geometrical deformations, especially when they are polymer-based. This can cause a mismatch between the experimental data and the expected theoretical performance; therefore, it is important to take thermal effects into account. The present paper investigates the influence of thermal deformations on the sound absorption of three geometries: a coplanar spiral tube, a system with double coiled resonators, and a neck-embedded resonator. Measurements were performed on each 3-D printed specimen in the impedance tube after the samples had been placed in a climate chamber to modify the temperature settings (T = 10–50 °C). Numerical models, validated on the measurements, were employed to quantify the geometrical deformation of AMM structures through a multiphysics approach, highlighting the effects of thermal stress on the acoustic behavior. The main outcomes prove that the frequency shifts of sound absorption peaks depend on temperature configurations and follow exponential regressions, in accordance with previous literature on polymeric materials.

Nowadays, opera houses are often used for symphonic music, even though the intrinsic characteristics of these theatres are not suited for this purpose, due to their coupled volumes and high absorption of the fly tower. When symphonic music is performed in these halls an overhead stage canopy is often used to enhance the orchestral performance. In the present work, the effects of a canopy array in a coupled volume theatre were studied. The array canopy was designed and installed based on Geometric Acoustic (GA) simulations calibrated with in-situ measurements. Results showed peculiar effects on the sound energy distribution through space: the sound strength values depends on the “effective” volume of the theatre, varying with the sound source position. Moreover, when the stage is covered by the canopy array, the sound strength depends on the distance from the aperture instead of the distance from the sound source position. In other words, the decay curve is “tilt” by “effective volume” and “shifted” by the canopy array. Furthermore, the changes in sound behaviour due to the canopy array may be considered as a switch-off of the secondary reverberation effect.